Method, apparatus and system for providing feedback to a transmit diversity device

ABSTRACT

A method and system for improving closed loop feedback in transmit diversity communication. In one embodiment of the invention, a predetermined variation of one or more transmit diversity parameters is performed at the transmit diversity transmitter. The receiver compares the transmit diversity parameter values of the received signals to the predetermined variation and transmits to the transmitter a value of a transmit diversity correction parameter. The transmitter may use this correction value to modify the transmit diversity parameter in a subsequent transmission.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/102,288, filed on May 6, 2011, now U.S. Pat. No.8,116,693,which is a continuation application of U.S. patent applicationSer. No. 12/046,689, filed on Mar. 12, 2008, now U.S. Pat. No.8,036,603, which claims the benefit of U.S. Provisional PatentApplication No. 60/918,066, filed on Mar. 15, 2007, all of which areincorporated in their entirety herein by reference.

FIELD OF THE INVENTION

This invention relates generally to the field of wireless communicationsand more specifically to providing feedback to a transmit diversitydevice.

BACKGROUND OF THE INVENTION

Wireless transmission systems may use transmit diversity, in whichsignals are transmitted to a receiver using a plurality of transmitantennas. A receiving communication device extracts the information fromthe transmitted signals. Multiple antenna elements may enhance spectralefficiency and capacity, allowing for more users to be simultaneouslyserved over a given frequency band, while reducing signal degradationcaused by multi-path and fading. Transmit diversity parameters may beapplied to signals transmitted from two or more antennas, and may modifyan effective power distribution detected by receivers, such as basestations. The transmitted signals may propagate along different pathsand may reach the receiving communication device with different phasesthat may destructively interfere. The received signal quality may changeat a receiver that may be attempting to detect a transmission from amobile terminal, as well as a noise level created by a wireless terminaltransmission in base stations attempting to detect signals from otherwireless terminals. A signal-to-noise ratio perceived by base stationsmay change with varying parameters of transmit diversity control. Thereis a need for a system, method, and apparatus to reduce interference oftransmitted signals.

US Patent Publication No. 2003/0002594, entitled “Communication devicewith smart antenna using a quality-indication signal,” published Jan. 2,2003 and assigned to the assignee of the present application, thecontents of which are incorporated herein by reference, describes usinga power control signal, for example, as provided by the power controlbit of the CDMA protocol, as a quality indication signal.

U.S. Pat. No. 5,999,826 (Whinnett) describes a method for remotereceiver determination of weights of a transmit diversity array by thereceiver being capable of identifying which received signal wastransmitted from which antenna. This method requires transmitting adifference reference signal from each antenna. The reference signals areeither tones, characterized by different carrier frequencies, differentmodulating frequencies (tones) or different digital codes. This methodrequires that the transmission of reference signals be defined by theair interface.

SUMMARY OF EMBODIMENTS OF THE INVENTION

In accordance with the present invention, disadvantages and problemsassociated with previous techniques for modifying transmit diversitysignals may be reduced or eliminated. In some embodiments of theinvention, the method, system and apparatus described in US PatentPublication No. 2003/0002594 may be improved, supplemented or replacedby those describe herein.

According to known methods of providing feedback to a transmit diversitytransmitter, an iterative process is taught in which a power control bitor other quality indication signal may be used to indicate whether, as aresult of a change of a diversity parameter, resultant power as measuredat the feedback communication device, for example, a base station, hasincreased or decreased. One benefit of embodiments of the presentinvention may be the elimination or reduction of iterations in order tocommunicate a desirable diversity parameter, for example, a phasedifference or a power ratio, from a base station to a transmit diversitymobile transmitter.

According to embodiments of the present invention, a mobile transmitdiversity transmitter may transmit according to a phase differencepattern, and the base station may measure received signals, performcalculations to determine phase difference correction value and/oramplitude ratio correction value, and transmit the value(s) to themobile station. The value(s) may be transmitted, for example, as acompressed binary value, a code from a codebook, or otherwise. Themobile station may then use this correction value to determine amodification to the transmit diversity parameter value in a subsequenttransmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is a block diagram illustrating one embodiment of a communicationsystem according to embodiments of the invention;

FIG. 2 is a schematic timeline of transmissions during a periodaccording to an embodiment of the invention; and

FIG. 3 is a schematic timeline of transmissions during a periodaccording to an embodiment of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Embodiments of the present invention and its advantages are bestunderstood by referring to FIGS. 1 through 3 of the drawings, likenumerals being used for like and corresponding parts of the variousdrawings.

FIG. 1 is a block diagram illustrating one embodiment of a communicationsystem 100 that includes a transmitter 110, also referred to as amodifying communication device, that that adjusts a nominal value of atransmit diversity parameter, for example, a phase difference or atransmission power ratio between a signal transmitted on a first antenna111 and a signal transmitted concurrently on a second antenna 112.According to the embodiment, transmitter may, for example, perturb asignal at a perturbation rate and transmit the signal to receivingcommunication device 120, also referred to as a feedback communicationdevice. Feedback communication device 120 may receive the transmitdiversity signal at antenna 121 and transmit/receive module 122, processthe received signal using processor 123, and transmit feedbackinformation that describes the signal as received by feedbackcommunication device 120. Modifying communication device 110 may adjusta nominal value of a transmit diversity parameter at a nominal valueadjustment rate based on the feedback information.

According to the illustrated embodiment, network 100 operates to provideservices such as communication sessions. A communication session mayrefer to an active communication between endpoints, measured fromendpoint to endpoint. Information is communicated during a communicationsession. Information may refer to voice, data, text, audio, video,multimedia, control, signaling, other information, or any combination ofthe preceding.

The information may be communicated in packets. A packet may comprise abundle of data organized in a specific way for transmission, and a framemay comprise the payload of one or more packets organized in a specificway for transmission. A packet-based communication protocol such asInternet Protocol (IP) may be used to communicate the packets.

Network 100 may utilize communication protocols and technologies toprovide the communication sessions. Examples of communication protocolsand technologies include those set by the Institute of Electrical andElectronics Engineers, Inc. (IEEE) 802.xx standards, InternationalTelecommunications Union (ITU-T) standards, European TelecommunicationsStandards Institute (ETSI) standards, Internet Engineering Task Force(IETF) standards, or other standards.

Devices of network 100 may use any suitable multiple access technology,for example, a code division multiple access (CDMA) technology.According to one embodiment, network 100 may operate according to a CDMA2000 telecommunications technology that uses a single CDMA channel. Asan example, a CDMA 2000 high rate data packet technology, such as theEvolution Data Only (EvDO) technology may be used.

Network 100 may comprise any suitable communication network. Acommunication network may comprise all or a portion of a public switchedtelephone network (PSTN), a public or private data network, a local areanetwork (LAN), a metropolitan area network (MAN), a wide area network(WAN), a global computer network such as the Internet, a wirelessnetwork, a local, regional, or global communication network, anenterprise intranet, other suitable communication link, or anycombination of the preceding.

A component of network 100 may include logic, an interface, memory,other component, or any suitable combination of the preceding. “Logic”may refer to hardware, software, other logic, or any suitablecombination of the preceding. Certain logic may manage the operation ofa device, and may comprise, for example, a processor. “Interface” mayrefer to logic of a device operable to receive input for the device,send output from the device, perform suitable processing of the input oroutput or both, or any combination of the preceding, and may compriseone or more ports, conversion software, or both. “Memory” may refer tologic operable to store and facilitate retrieval of information, and maycomprise a Random Access Memory (RAM), a Read Only Memory (ROM), amagnetic drive, a disk drive, a Compact Disk (CD) drive, a Digital VideoDisk (DVD) drive, a removable media storage, any other suitable datastorage medium, or a combination of any of the preceding.

Communication network 100 may include one or more modifyingcommunication devices 110 and one or more feedback communication devices120 that communicate via a wireless link 130. Either or both ofcommunication devices 110 and 120 may be any device operable tocommunicate information via signals with one or more other communicationdevices. For example, either of communication devices 110 or 120 maycomprise a mobile subscriber unit or a base station. A subscriber unitmay comprise any device operable to communicate with a base station, forexample, a personal digital assistant, a cellular telephone, a mobilehandset, a computer, or any other device suitable for communicatingsignals to and from a base station. A subscriber unit may support, forexample, Session Initiation Protocol (SIP), Internet Protocol (IP), orany other suitable communication protocol.

A base station may provide a subscriber unit access to a communicationnetwork that allows the subscriber unit to communicate with othernetworks or devices. A base station typically includes a basetransceiver station and a base station controller. The base transceiverstation communicates signals to and from one or more subscriber units.The base station controller manages the operation of the basetransceiver station.

In some embodiments of the invention, the feedback communication device120 may be a base station, and the modifying communication device 110may be a subscriber unit.

Either or both of communication devices 110 or 120 may include one ormore antenna elements, where each antenna element is operable toreceive, transmit, or both receive and transmit a signal. Multipleantenna elements may provide for a separation process known as spatialfiltering, which may enhance spectral efficiency, allowing for moreusers to be served simultaneously over a given frequency band.

A communication link between communication devices 110 and 120 such aswireless link 130 may be a radio frequency link that is cellular innetwork organization. Wireless link 130 may be used to communicate asignal between communication devices 120 and 110.

As described more fully below, according to embodiments of the presentinvention, modifying communication device 110 may include a processor114 and a transmit/receive module 113 that calculate and produce one ormore signals for transmission over at least first and second antennas111 and 112.

Feedback communication device 120 may include a processor 123 andtransmit/receive module 122 that generate and transmit a feedback signalthat indicates the quality of the modified signal as received at thefeedback communication device 120. Modifying communication device 110may then modify the transmit signal in accordance with feedbackinformation corresponding to the feedback signal.

According to one embodiment, modifying a signal may refer to modifying asignal feature. A transmission signal feature, or in some embodiments ofthe invention, a transmit diversity parameter, may refer withoutlimitation to any feature of the transmission, for example, relativephase, relative amplitude, relative power, absolute power, frequency,timing, other suitable signal feature that may be modulated, or anycombination of the preceding. Relative phase may refer to the phasedifference between the phase of a first signal of a first transmitantenna element and the phase of a second signal of a second transmitantenna element. Relative power may refer to the ratio between the powerof a first signal of a first transmit antenna element and the power of asecond signal of a second transmit antenna element, which ratio may bedefined on a linear or logarithmic scale. Relative amplitude may referto the ratio between the amplitude of a first signal of a first transmitantenna element and the amplitude of a second signal of a secondtransmit antenna element. Absolute power may refer to the total powertransmitted by all antennas of modifying communication device 110.According to one embodiment, modifying a signal may be described asadjusting a nominal value of a transmit diversity parameter. Asdescribed more fully herein, according to an embodiment of theinvention, modulation of a transmit diversity parameter during aperturbation cycle may comprise transmitting using a transmit diversityparameter deviating from the nominal value in a first direction during afirst portion of the perturbation cycle and then transmitting using atransmit diversity parameter deviating from the nominal value in asecond direction during a second portion of the perturbation cycle.

According to one embodiment of operation of the invention, modifyingcommunication device 110 may modify a signal by perturbing the signal.Perturbing a signal may refer to modulating a signal feature of thesignal in relation to a nominal value of the signal, for example,modifying the signal feature in a first direction for a first feedbackinterval, and in a second direction for another feedback interval. Aperturbation cycle may refer to a first modulation in a first directionand a second modulation in a second direction. In some embodiments ofthe invention, a perturbation cycle may comprise a different, forexample, longer or more complex, sequence of modulations. As an examplewith respect to phase, a perturbation may include modulating the phasedifference in a first direction, and modulating the phase difference ina second direction. If the feedback information provided by the feedbackcommunication device 120 indicates an improvement in the signal receivedusing one perturbation modulation direction compared to the signalreceived using the other perturbation modulation direction, the nextnominal value adjustment may be made in the improved direction in anamount less than or equal to the modulation.

According to embodiments of the invention, the nominal value of atransmit diversity parameter may be perturbed at a first rate,designated the perturbation rate, and the nominal value of the transmitdiversity parameter may be adjusted at a second rate, designated thenominal value adjustment rate. The perturbation rate and the nominalvalue adjustment rates may be the substantially the same or they may bedifferent, and each one may be substantially the same or different thanthe feedback rate.

According to an embodiment of the present invention, the transmitdiversity transmitter, for example, a mobile device with a plurality ofantennas, may transmit a first signal and a second signal, each signalhaving equal amplitude, using the respective antennas. The first andsecond signals may be transmitted sequentially with a perturbation inthe phase differences between the transmitting antennas. Thus, forexample, a signal may be transmitted over the antennas first using afirst phase difference, and then a signal may be transmitted using asecond phase difference, perturbed from the first phase difference. Thesignals are transmitted over carrier angular frequency ω.

The signals may be received at a receiver, for example, a base station.At the receiver, the signals may be received with different amplitudes,for example, due to difference in path loss and/or potential imbalanceat the mobile station. The relative or normalized amplitude of thesecond received signal relative to the first received signal is denotedA. The two signals may also be received with different phases, forexample, due to the intentional phase difference introduced at thetransmitter as well as due to the differences in effective propagationpaths, wherein the difference in received phase is denoted φ. Thus, thesignal from the first antenna is received by the base station as s₁(t),and the signal from the second antenna as s₂(t). Here, s₁(t) and s₂(t)denote signals received by the base station and illustrate maximumcombined amplitude received when their phase difference φ is zero.

It will be readily evident that in the following equations, thefollowing conventions are used for the notation of trigonometric andother functions:

-   -   sin(x) is the sine function of x;    -   cos(x) is the cosine function of x;    -   tg(x) is the tangent function of x;    -   argtg(x) is the arc-tangent function of x;

$\frac{\partial f}{\partial x}$is the partial derivative of the function f relative to the variable x;and

$\frac{\partial^{2}f}{\partial x^{2}}$is the partial second derivative of the function f relative to thevariable x.

The two received signals may combine at the base station to form s(t),and therefore:s ₁(t)=sin(ωt)  (1)s ₂(t)=A sin(ωt+φ)  (2)s(t)=s₁(t)+s ₂(t)  (3)

$\begin{matrix}\begin{matrix}{{s(t)} = {{\sin\left( {\omega\; t} \right)} + {A\;{\sin\left( {{\omega t} + \varphi} \right)}}}} \\{= {{\sin\left( {\omega\; t} \right)} + {A\left\lbrack {{{\sin\left( {\omega\; t} \right)}\;{\cos(\varphi)}} + {{\cos\left( {\omega\; t} \right)}{\sin(\varphi)}}} \right\rbrack}}} \\{{= {{{B(\varphi)}{\sin\left( {\omega\; t} \right)}} + {{C(\varphi)}{\cos\left( {\omega\; t} \right)}}}},}\end{matrix} & (4)\end{matrix}$whereB(φ)=1+A cos(φ)C(φ)=A sin(φ)  (5)

Therefore, it will be recognized that:s(t)=B(φ)[sin(ωt)+D(φ)cos(ωt)],  (6)where

$\begin{matrix}{{D(\varphi)} = {\frac{C(\varphi)}{B(\varphi)} = {{{tg}(\gamma)} = {{\frac{\sin(\gamma)}{\cos(\gamma)}.{So}}\text{:}}}}} & (7) \\{{s(t)} = {\frac{B(\varphi)}{\cos(\gamma)}\left\lbrack {{{\cos(\gamma)}{\sin\left( {\omega\; t} \right)}} + {{\sin(\gamma)}{\cos\left( {\omega\; t} \right)}}} \right\rbrack}} & (8)\end{matrix}$

Or the final expression for the signal received by the base station canbe written as:

$\begin{matrix}{{s(t)} = {\frac{B(\varphi)}{\cos(\gamma)}{\sin\left( {{\omega\; t} + \gamma} \right)}}} & (9)\end{matrix}$

Therefore, for the model of two transmitted sinusoids, the signalreceived by the base station is also a sinusoid with the same frequencybut different amplitude and phase. γ depends on the basic variables Aand φ, defined above in (1):

$\begin{matrix}{{\gamma = {{{arc}\;{{tg}\left\lbrack \frac{C(\varphi)}{B(\varphi)} \right\rbrack}} = {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}}}},} & (10)\end{matrix}$and the final expression of the received signal may thus be written as afunction of the unknown variables A, φ:

$\begin{matrix}{{s(t)} = {\frac{1 + {{Acos}(\varphi)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}} \right)}{{\sin\left( {{\omega\; t} + {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}}} \right)}.}}} & (11)\end{matrix}$

Assuming a transmit cycle of duration T, known to both the transmitterand receiver, for example, to the mobile station and to the basestation, where the mobile transmits with a nominal phase during periodT₁, then introduces a phase perturbation of α₁ for a period of T₂,followed by a phase perturbation of α₂ for a period of T₃. From (11), itmay be deduced that the signal has an amplitude AMP, where:

$\begin{matrix}{{{AMP} = \frac{1 + {{Acos}(\varphi)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}} \right)}},} & (12)\end{matrix}$and phase PH, where:

$\begin{matrix}{{PH} = {{arc}\;{{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}.}}} & (13)\end{matrix}$

FIG. 2 depicts a period T according to an embodiment of the invention inwhich perturbed signals T₂ and T₃ appear after T₁, which has longerduration. It will be noted that from a processing delay point of view,the timing of T₂ and T₃ in the cycle, for example, at the end, middle orbeginning of the cycle, may shorten the overall system delay. In oneembodiment of the invention, T₁ may be approximately 90% of total periodT, and each of T₂ and T₃ may be 5% of total period T.

Because these time periods are known at both the base station and themobile station, amplitudes and phases may be compared for the times T₁,T₂, and T₃ as follows:

$\begin{matrix}{{{For}\mspace{14mu} T_{1}\text{:}}{{{AMP}\left( T_{1} \right)} = \frac{1 + {{Acos}(\varphi)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}} \right)}}} & (14) \\{{{PH}\left( T_{1} \right)} = {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}}} & (15) \\{{{For}\mspace{14mu} T_{2}\text{:}}{{{AMP}\left( T_{2} \right)} = \frac{1 + {{Acos}\left( {\varphi + \alpha_{1}} \right)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \alpha_{1}} \right)}{1 + {{Acos}\left( {\varphi + \alpha_{1}} \right)}} \right\rbrack}} \right)}}} & (16) \\{{{PH}\left( T_{2} \right)} = {{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \alpha_{1}} \right)}{1 + {{Acos}\left( {\varphi + \alpha_{1}} \right)}} \right\rbrack}}} & (17) \\{{{For}\mspace{14mu} T_{3}\text{:}}{{{AMP}\left( T_{3} \right)} = \frac{1 + {{Acos}\left( {\varphi + \alpha_{2}} \right)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \alpha_{2}} \right)}{1 + {{Acos}\left( {\varphi + \alpha_{2}} \right)}} \right\rbrack}} \right)}}} & (18) \\{{{PH}\left( T_{3} \right)} = {{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \alpha_{2}} \right)}{1 + {{Acos}\left( {\varphi + \alpha_{2}} \right)}} \right\rbrack}}} & (19)\end{matrix}$

The case where α₂=−α₁ is a special symmetric perturbation case of theabove.

Using the above equations, a new value for φ is sought that willmaximize the AMP function given the set of measured parameters y₁through y₄:

$\begin{matrix}{y_{1} = \frac{{AMP}\left( T_{2} \right)}{{AMP}\left( T_{1} \right)}} & (20) \\{y_{2} = \frac{{AMP}\left( T_{3} \right)}{{AMP}\left( T_{1} \right)}} & (21)\end{matrix}$y ₃=γ(T ₂)−γ(T ₁)=PH(T ₂)−PH(T ₁)  (22)y ₄=γ(T ₃)−γ(T ₁)=PH(T ₃)−PH(T ₁)  (23)

By using the ratio of amplitudes, the unknown scaling may be canceled.

Accordingly, variables A and φ may be determined as the values that bestfit the set of equations (24)-(27) as follows:

$\begin{matrix}{y_{1} = \frac{\frac{1 + {{Acos}\left( {\varphi + \alpha_{1}} \right)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \alpha_{1}} \right)}{1 + {{Acos}\left( {\varphi + \alpha_{1}} \right)}} \right\rbrack}} \right)}}{\frac{1 + {{Acos}(\varphi)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}} \right)}}} & (24) \\{y_{2} = \frac{\frac{1 + {{Acos}\left( {\varphi + \alpha_{2}} \right)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \alpha_{2}} \right)}{1 + {{Acos}\left( {\varphi + \alpha_{2}} \right)}} \right\rbrack}} \right)}}{\frac{1 + {{Acos}(\varphi)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}} \right)}}} & (25) \\{y_{3} = {{{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \alpha_{1}} \right)}{1 + {{Acos}\left( {\varphi + \alpha_{1}} \right)}} \right\rbrack}} - {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}}}} & (26) \\{y_{4} = {{{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \alpha_{2}} \right)}{1 + {{Acos}\left( {\varphi + \alpha_{2}} \right)}} \right\rbrack}} - {{arc}\;{{tg}\left\lbrack \frac{{Asin}(\varphi)}{1 + {{Acos}(\varphi)}} \right\rbrack}}}} & (27)\end{matrix}$

The estimation of best fit values for A and φ may be carried out usingwell-known numerical methods that need not be detailed herein. Once Aand φ are known, a correction β may be determined by maximizing thefollowing AMP(T′):

$\begin{matrix}{{{AMP}\left( T^{\prime} \right)} = \left. {\frac{1 + {{Acos}\left( {\varphi + \beta} \right)}}{\cos\left( {{arc}\;{{tg}\left\lbrack \frac{{Asin}\left( {\varphi + \beta} \right)}{1 + {{Acos}\left( {\varphi + \beta} \right)}} \right\rbrack}} \right)}}\Rightarrow\max \right.} & (28)\end{matrix}$i.e., from the set (29)

$\begin{matrix}{{\frac{\partial{{AMP}\left( T^{\prime} \right)}}{\partial\beta} = 0}{\frac{\partial^{2}{{AMP}\left( T^{\prime} \right)}}{\partial\beta^{2}} < 0}} & (29)\end{matrix}$

The value of β may be computed by standard numerical evaluation of theformula to determine its maximum, or from a look-up table, or from anymathematically available closed formula. The mathematical derivation of(29) shows that AMP(T′) is at a maximum when:β=−φ  (30)and the maximum value ismax{AMP(T′)}=1+A  (31)

The base station may therefore transmit to the mobile station thenumerical value of β, as calculated above. The mobile station maycorrect the previous nominal phase difference between a signaltransmitted through its antenna ports by β, so the present phasedifference φ becomes φ+β. It will be recalled that φ represents thephase difference received at the phase difference, which isapproximately the phase difference transmitted plus a phase differencedue to the propagation path.

Additionally or alternatively, in an embodiment of the invention, oneperiod may be transmitted with a certain phase difference and powerratio, and a subsequent period may be transmitted based on the lastcontrol of the base station so no perturbation is required, as shown inFIG. 3. Since the above computation provided four measurements tocompute two unknowns, the same math applies here.

In an embodiment of the invention, which may produce further accuracy,the base station may use a number of measurements of previous cycles toprovide a more robust solution in terms of signal-to-noise ratio (SNR),at the expense of higher sensitivity to mobility due to the longerhistory used.

In yet another embodiment of the invention, the base station may provideinformation to the mobile station for the correction of the amplituderatio, i.e. the relative power division of the transmitted signalsbetween the antenna ports of the mobile station, so as to maximize thereceived signal.

In actual implementation of this invention, it should be taken intoaccount that there may be apparent frequency differences among thesignal transmitted by the mobile station, the signal received by thebase station, and the internal frequency reference of the base station.Since the invention of the present application may include estimation ofphase differences at different times, differences in frequency betweenthe estimator and the signals being estimated may induce atime-dependent phase difference Δφ(t) related to the differences inangular frequency Δω and the elapsed time Δt:Δφ(t)=ΔωΔt  (32)

The base station may therefore estimate the phase difference or phasedrift and compensate for it after estimating the frequency differencebetween the signal it receives and its internal time reference. Thesesolutions are well known to those versed in the art.

In an embodiment of the invention, the base station may providecorrection for both phase and amplitude ratio of the transmitted signalsso as to maximize the received signal.

In yet another embodiment of this invention, the base station mayestimate the future optimal phase difference or optimal amplitude ratiocommunicated to the base station using standard linear or non-linearprediction techniques well known to those versed in the art. This meansthat rather than send the result computed based on past signals asdescribed in (30) and above, a predictor is applied to determine whatshould be the optimal parameters by the time they are applied by themobile station.

In yet another embodiment of this invention, the base station sendscorrection parameters and the mobile station determines what parametersshould be applied by applying linear or non-linear prediction techniqueswell known to those versed in the art. This embodiment may be optimizedby knowing the times to which the base station computations refer, whichmay be set up by an agreement or standard.

In yet another embodiment of this invention, the mobile may correct theparameters it applies by measuring variations in the downlink signal itreceives from the base station. This allows the mobile station toimmediately apply a compensation for variations caused, for example, bythe mobile rotation, change in position or change in velocity relativeto the base station. These corrections are applied by using the sameestimation techniques as required for the previous embodiment, includingestimation of frequency difference and application of the requiredchanges per the time period. When combined with the dual antennareception in the mobile station, changes in the amplitude of the signalsreceived by the two antennas may be applied to the amplitude ratio ofthe transmitted signal.

Corrections introduced by the mobile station by means of prediction ormeasurements of the downlink signals it receives may be applicable toany application of transmit diversity control in the mobile station,whether based on provision of transmit diversity control parameters(phase difference or amplitude) by the base station or transmitdiversity control parameters computed by the mobile station using thisor other inventions, for example, power control based.

Although the various embodiments were described related to the uplinktransmit diversity control, the roles of the base station and mobilestation may be reversed so as to apply the teachings of the presentinvention to downlink transmit diversity control.

Certain embodiments of the invention may include none, some, or all ofthe above technical advantages. One or more other technical advantagesmay be readily apparent to one skilled in the art from the figures,descriptions, and claims included herein.

The previous description of the embodiments is provided to enable anyperson skilled in the art to make or use the invention. While theinvention has been particularly shown and described with reference toembodiments thereof, it will be understood by those skilled in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention. For example, anymobile communication protocol may be used, for example, CDMA or othertypes of protocols. For example, the communication devices similar tothose described above can be used with time-division multiple access(TDMA) or frequency-division multiple access (FDMA) protocols. Such aTDMA protocol can include, for example, the Global Systems for MobileCommunications (GSM) protocol.

Note that although the tuning of a communication device is describedthrough the use complex weighting, in other embodiments other types ofcontrol signals may tune the communication device. In other words, thetuning of a communication device through the use of such control signalsneed not be limited to information about varying the magnitude and phaseof the signal. For example, the control signals may carry information tovary the magnitude, phase, frequency and/or timing of the signalassociated with each antenna element.

While various embodiments of the invention have been described above, itshould be understood that they have been presented by way of exampleonly, and not limitation. Thus, the breadth and scope of the inventionshould not be limited by any of the above-described embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1. A method of using feedback by a transmit diversity mobilecommunication device comprising: transmitting by a mobile communicationdevice a plurality of signals to a base station, said plurality ofsignals transmitted by a plurality of antennas using a phase difference;receiving from said base station a phase difference correction based onsaid transmitted plurality of signals, wherein the phase differencecorrection is in a form selected from the group consisting of acompressed binary value and a code from a codebook; and calculating amodified phase difference based on the received phase differencecorrection; and transmitting by the mobile communication device on saidplurality of antennas a modified signal using said modified phasedifference, wherein the signals transmitted on each of the antennasdiffer by the modified phase difference.
 2. The method of claim 1,wherein transmitting said plurality of signals to the base stationcomprises transmitting a first plurality of signals from the mobilecommunication device using at least two antennas, wherein thetransmitted signals on each of the antennas differ by a first phasedifference.
 3. The method of claim 2, wherein calculating the modifiedphase difference comprises calculating the modified phase differencebased on the first phase difference and the phase difference correction.